When installing a gas furnace and evaporator coil or an air handler on their side if the unit is not being suspended then you should include these noise reducing styrofoam risers. 

Highlights: 

1. Light weight and easy to handle.
2. Four foot long blocks that can be easily cut to size to fit most installations.
3. Reduces noise being transmitted to the level below by reducing vibration.
4. If you are using a secondary drain pan you need to create separation between the bottom of the equipment and the drain pan. These blocks provide an easy to use, water proof, and mold resistant solution.
5. Can be used with standard and high efficiency natural gas/LP furnaces, air handlers, modular blowers, and evaporator coils.
6. Either 4 or 6 inches tall depending on the installation.
7. Helps to create space for proper condensation removal for high efficiency furnaces, air handlers, and evaporator coils.
8. Can be used with concealed duct air handlers if suspending the air handler isn't an option. 

Dimensions:

Width - 4 in

Height - 6 in

Length - 48 in